macbu.c

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#define X   0
#define Y   1
 
/* shoot a test ray along +X axis - macmartinized by me, a bit messier */
int macmartintest( pgon, numverts, point )
double  pgon[50000][2] ;
int numverts ;
double  point[2] ;
{
int inside_flag, xflag0 ;
double  *p, *stop ;
int crossings ;
double  tx, ty, y ;
 
    crossings = 0 ;
 
    tx = point[X] ;
    ty = point[Y] ;
    y = pgon[numverts-1][Y] ;
 
    p = (double *)pgon + 1 ;
    if ( ( y >= ty ) != ( *p >= ty ) ) {
        /* x crossing */
        if ( ( xflag0 = ( pgon[numverts-1][X] >= tx ) ) ==
         ( *(double *)pgon >= tx ) ) {
 
        if ( xflag0 ) crossings++ ;
        } else {
        /* compute intersection of pgon segment with X ray, note
         * if > point's X.
         */
        crossings += ( pgon[numverts-1][X] -
        (y-ty)*( *(double *)pgon - pgon[numverts-1][X])/(*p-y)) >= tx ;
        }
    }
 
    stop = pgon[numverts] ;
 
    for ( y=*p,p += 2 ; p < stop ; y=*p,p+=2) {
 
        if ( y >= ty ) {
        while ( (p < stop) && (*p >= ty) ) p+=2 ;
        if ( p >= stop ) goto Exit ;
        /* y crosses */
        if ( ( xflag0 = ( *(p-3) >= tx ) ) ==
             ( *(p-1) >= tx ) ) {
 
            if ( xflag0 ) crossings++ ;
        } else {
            /* compute intersection of pgon segment with X ray, note
             * if > point's X.
             */
            crossings += ( *(p-3) -
            (*(p-2)-ty)*( *(p-1)-*(p-3))/(*p-*(p-2))) >= tx ;
        }
        } else {
        while ( (p < stop) && (*p < ty)) p+=2 ;
        if ( p >= stop ) goto Exit ;
        /* y crosses */
        if ( ( xflag0 = ( *(p-3) >= tx ) ) ==
             ( *(p-1) >= tx ) ) {
 
            if ( xflag0 ) crossings++ ;
        } else {
            /* compute intersection of pgon segment with X ray, note
             * if > point's X.
             */
            crossings += ( *(p-3) -
            (*(p-2)-ty)*( *(p-1)-*(p-3))/(*p-*(p-2))) >= tx ;
        }
        }
    }
 
    Exit:
    /* test if crossings is odd */
    /* if we care about is winding number > 0, then just:
           inside_flag = crossings > 0 ;
     */
    inside_flag = crossings & 0x01 ;
    
    return (inside_flag) ;
}